45, COENHILL, E.G., AND 122, KEGENT STREET, W., LONDON. 63 



NEGRETTI & ZAMBRA'S 



NEW PATENT STANDARD 



MARINE REGISTERING THERMOMETERS.* 



81. " The most'successful Deep- Sea Thermometer hitherto has been Six's Thermometer, 

 with the bulb protected from pressure, as invented by NEGRETTI AND ZAMBRA in 1867. 

 Nevertheless there are several disadvantages inherent in the principle of construction of Six's 

 instrument. The indices are unreliable, as, however carefully fitted, they may slip down by 

 gravity, and even shift upward by sudden lifting motion ; so that the observations are 

 always more or less liable to error : the index error also is very liable to alter by the shifting 

 of the spirit, or by bubbles of spirit getting among the mercury ; and unless the observer is 

 well-trained in its management, and takes care to compare it with a correct ordinary ther- 

 mometer every time it is used, there is no guaranteeing 1 its accuracy of indication. Further, 

 its accuracy in its best condition does not attain to fractions of a degree, as it cannot be 

 read off closer than about half a degree. Then it must be kept in the vertical position, or 

 it is certain to become more or less deranged in transit. 



" However, so long as it sufficed to observe the nearest degree of temperature, the 

 improved protected Six's answers the purpose of a deep-sea thermometer, with careful 

 management and checking ; but lately the bottom temperature of shallow seas and of rivers 

 has come under investigation, and for this purpose Six's instrument is unsuitable. 



" Between the temperature of the surface of the sea and that at the depth of a few 

 fathoms, the differences to be determined are found to be not degrees of the thermometer, 

 but fractions of a degree ; hence, the observations to be worth anything at all, must be made 

 with an undoubtedly accurate thermometer. 



" During the last two or three years systematic observations of the surface and bottom 

 temperatures have been taken from the various lightships off the British coasts, under the 

 direction of the Meteorological Office. This investigation of the temperatures of the British 

 seas has been urged upon the Government by naturalists and physicists interested in the 

 question of the food supply of the people as affected by the take of fish. What is required 

 to be made evident is, whether any, and what, effect temperature has upon the habits and 

 migrations of fish, so as to tend to a right understanding of the conditions favourable for 

 the development of the various species of fish, and the best seasons and temperature indi- 

 cations for their capture. This investigation, commenced with Six's Thermometers, has at 

 present only shown that such instruments are not sufficiently reliable for the purpose ; and 

 it was represented by the Government to Messrs NEGRETTI AND ZAMBRA, that a more 

 perfect and stable deep-sea thermometer was a desideratum. They accordingly turned their 

 attention to the matter, and the result is the new STANDARD DEEP-SEA THERMOMETER. 



" The construction of this thermometer will be readily understood by reference to the 

 sketch diagram fig. 71. The bulb is cylindrical, and mercury is the thermometrical fluid. 

 The neck of the bulb is contracted in a peculiar manner at A, and upon the shape and fine- 

 ness of this contraction the success of the instrument mainly depends. Beyond A the tube 

 is bent, and a small catch reservoir is formed at B, for a purpose to be present/I^ explained. 

 At the end of the tube a small receptacle, C, is provided. When the tube is downward, the 

 glass contains sufficient mercury to fill the bulb, tube, and a part of the reservoir C, if the 

 temperature is high, leaving sufficient space in C for the expansion of the mercury. In this 

 position no scale would be possible, as the apparent movement of the mercury would be 

 confined to the space C. When the thermometer is held bulb upward, the mercury breaks 

 off at A, but by its own weight flows down the tube, filling C and a portion of the tube above 

 C, in relation to the resisting temperature. The scale accordingly is made to read upwards 

 from C. To set the instrument for observation it is only necessary to place it bulb down- 



* Description condensed from " ENGINEERING," Mai-ch 22iid, 1878. 



